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What Are Rocks and Minerals?
Rocks: You have probably walked on them, ridden over them, and
even eaten them! But if you had to describe them to someone, what
would you say?
MINERALS
IN
ROCKS
To read the story of a rock, you have to know something about the
substances that are part of it. If you examine a rock closely, you will
notice it is made up of many little particles called grains. The
appearance and properties of a rock depend on the nature of these
many grains and the particular materials of which they are made.
The building blocks of rock are pure, naturally occurring solid
materials called minerals. All rocks are made of minerals. Some
rocks, such as limestone, are formed of only one mineral, while
others, such as granite, are made up of several different minerals.
G i v e i t a TRY
A
C
T
I
V
I
T
info BIT
Rock Products
An area of the Bow
Valley in the Rocky
Mountains near
Exshaw, Alberta, is
mined for limestone.
This mineral is used to
make a variety of
products, from
stomach relief tablets
that relieve upset
stomachs, to concrete.
Y
MISSION CONTROL, THIS IS …
Pathfinder was a robot vehicle sent by NASA to investigate and gather
information from the surface of Mars. Imagine you are with Pathfinder, and
you must transmit a description of the rocks and minerals you’ve found on
the planet’s surface. Use a hand lens or magnifying glass to study the rock
samples your teacher gives you. (Be sure to wash your hands after
handling the rocks.) Describe each one using words or pictures, and use
the following questions to help you with the description.
• What colour is the sample? Is it the same colour all around? (Wet the
surface and see if the colour changes.)
• Does it have a smell?
• What does the surface feel like?
• Is it living or non-living?
• Does it seem to be made up of one substance or a combination of
several others?
• Are any of the samples similar to each other?
• What else can you say about these samples?
Figure 2.2 Mars Pathfinder
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You may have heard the names of common minerals, such as
quartz and mica. In fact, more than 3500 different minerals have
been identified. However, you don’t have to recognize or know all
of them to identify most of the rocks you’ll find. Just five minerals
combine in different ways to form the majority of the rocks in
Earth’s crust. These minerals are:
• calcite
• quartz
• feldspar
• mica
• hornblende
Figure 2.3
quartz
mica
calcite
feldspar
hornblende
info BIT
Rock Crystals
Crystals form when the particles in a mineral line up in a regular
pattern that creates smooth surfaces and sharp edges. Each
mineral has its own, unique crystal pattern. Crystals that cool
slowly, for example, will form bigger crystals than those that
cool quickly. Halite (common table salt) forms cubes. Quartz
forms long, six-sided crystals with a pointed end. What kind of
conditions do you think a mineral would need to allow it to
grow into a crystal?
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Halite crystal
(sodium chloride)
Quartz
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USING PROPERTIES
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TO IDENTIFY
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MINERALS
To identify rocks, you need to identify the minerals they contain.
Because many of the same rocks and minerals are found in different
parts of the world, geologists have developed a series of
classifications for describing their properties. Properties are the
features that a material or object has. For minerals, some important
properties are:
• colour
• lustre
• streak
• cleavage
• fracture
• hardness
Knowing only one of these properties is usually not enough for you
to identify the mineral. You need to look at a combination of these
properties. Think of this process as a jigsaw puzzle: one piece does
not give you the whole picture. (See Figure 2.4 for some examples.)
Colour
Colour is a useful starting point because it’s the first property you
notice.
Lustre
Lustre is the way the surface of a mineral reflects light. Some
minerals have a metallic lustre. This means they are shiny like
metals, such as gold or silver. Even though two minerals may have
the same colour, their lustre may help to tell them apart. Other
words to describe a mineral’s lustre are pearly, glassy, waxy, silky,
greasy, and brilliant.
Streak
A mineral’s streak is the colour of the powder that it leaves behind
when you rub it across a rough surface. The colour of the streak is
not always the same as the colour of the mineral. Usually,
geologists use an unglazed ceramic tile (like the tile used on
bathroom walls, but not shiny). They scratch a mineral sample on
the plate, and the colour of that streak gives a clue as to the
mineral’s identity.
Cleavage and Fracture
If you drop or break a mineral, you may notice the sample will
break in a certain way. If a mineral splits easily into two smooth
surfaces, this can be described as cleavage. In contrast to cleavage,
fracture is a mineral breakage with rough and uneven surfaces.
(However, any mineral can be fractured if enough force is applied.)
Figure 2.4 Properties of
different minerals
The colour of amber is yellow.
The lustre of native copper is shiny.
Jade makes a white streak.
Mica is a mineral that cleaves
easily into flat sheets.
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Hardness
The hardness of a mineral is measured by how easily it can be
scratched. The harder mineral leaves a scratch on the softer one.
The relative hardness of a mineral is measured with a scale
developed by a German scientist, named Frederic Mohs. Mohs scale
of hardness consists of 10 minerals ranked in order of hardness.
The scale is described below and in Figure 2.5.
The hardness of quartz is 7.
Mohs Scale of Hardness
Scale
1
2
3
4
5
6
7
8
9
10
1
2
Figure 2.5 The hardness
scale is a guide to
identifying minerals. Each
mineral can scratch all
the minerals with a lower
scale ranking than its
own.
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can be scratched
with a fingernail
7
can’t be scratched with
a knife but it may barely
scratch glass
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Can Be Scratched With
talc (softest)
gypsum
calcite
fluorite
apatite
feldspar
quartz
topaz
corundum
diamond (hardest)
soft pencil point
fingernail
copper wire
iron nail
glass
steel file
sandpaper
sandpaper
emery board
diamond
3
very easily scratched
with a fingernail
6
Mineral
4
very easily scratched
with a knife
8
scratches glass
easily
scratches glass very
easily and scratches
a steel file
5
easily scratched
with a knife
9
hard to scratch
with a knife
10
cuts glass and scratches a steel file
IDENTIFYING MINERALS
The first step in identifying a rock is determining what minerals it
contains. This is not always an easy task as two rocks can have
exactly the same minerals in them, yet they may look different
because they formed in different ways. However, if you use the six
properties of minerals, the Mohs scale of hardness, and a good
database of mineral characteristics, you can identify most rocks.
Careers
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Profiles
and
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VOLCANOLOGIST
It’s Monday, and you’re back on the job ... but where are you?
You’re walking over a rocky black mountain and it’s rumbling
gently under your feet! A few metres away, you can see jets of
smoke coming from cracks in the rock. Oh no! It’s a volcano!
But instead of running, you haul out your instruments and set
them up. This is your job: you’re a volcanologist.
Volcanologists study volcanoes. They measure the
movement in volcanoes to see if they’re going to erupt. When
an eruption occurs, they watch carefully to see how it happens.
They also study the way lava comes out of a volcano and how it
moves. The most serious part of their job is predicting whether
or not a particular volcano will erupt. If they are right, many
lives could be saved.
Figure 2.6 Volcanologists taking samples from a
lava tube on the island of Hawaii
Seismologist
Seismologists study earthquakes. They watch carefully for
changes in Earth’s surface, like twisting or moving rocks.
Devices such as the seismograph are used to record the shaking
and trembling of an earthquake. Yet even though seismologists
know the areas of earthquake activity, they unfortunately can’t
predict when and where earthquakes will occur.
Another important part of a seismologist’s job is to make
sure buildings are earthquake-safe. Buildings made of brick
often fall apart in an earthquake. It is better to have a building
with a steel or wooden frame. Seismologists teach people in
earthquake areas how to be safe in case of danger.
1. What does the work of volcanologists
tell us about Earth’s structure?
2. In what areas in Canada might you
Figure 2.7 Seismographs record movement deep
expect to find seismologists at work?
inside Earth.
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Inquiry
Activity
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PROSPECTING
FOR
MINERALS
The Question
How can you identify a mineral by its properties?
The Hypothesis
Materials & Equipment
Develop a hypothesis based on the question above.
• samples of known
minerals
• hand lens
• streak plate
• copper wire
• iron nail
• sandpaper
• samples of unknown
minerals
• database of minerals (or a
rock and mineral field
guide)
Figure 2.8 Step 6. Use a hand lens to examine the mineral’s structure.
Procedure
Part 1
1 Choose a sample of a known mineral, and record its number and name in
your chart. (See the chart example on the opposite page.)
2 Record its colour in your chart.
3 Describe its lustre as metallic (shiny like metal) or non-metallic. If it’s non-
metallic, try to describe it in another word. For example, if it looks like glass,
you could describe it as “glassy.”
4 Scrape the sample across the streak plate. Brush off the loose powder with
your fingers. If there is a streak, record its colour.
5 To test hardness, start by scratching the sample with your fingernail. If it
doesn’t leave a scratch or groove on the sample, try the copper wire. If the
wire doesn’t leave a scratch or groove, try an iron nail. Then try the
sandpaper. Record the hardness of the sample. (It might be between two
numbers on the hardness scale, so you could rank it as 4–5 or 6–7.)
6 Use a hand lens to examine the mineral’s structure.
7 Add any other information that you’ve observed about the mineral. Record
this in your “Other” column.
8 Repeat steps 1 to 7 with the other samples of known minerals.
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Part 2
8 For each unknown mineral, record its number in your chart.
9 Repeat steps 2 to 6 from Part 1 of the procedure for each unknown mineral.
10 Use the information in your database of known minerals to identify your
unknown samples. Enter the name of the mineral in the “Mineral Name”
column.
Collecting Data
11 Use a chart like the one below to record the information about the properties
of each mineral sample.
Mineral
ID No.
Mineral
Name
Colour
Lustre
Streak
Hardness
Other
Analyzing and Interpreting
12 Is colour a reliable property to use for identifying minerals? Why or why not?
13 Which property or properties did you find the most useful for identifying
minerals? Why?
Forming Conclusions
14 Write a summary paragraph that answers the question: “How can you identify
a mineral by its properties?”
Applying and Connecting
Can you think of another way to display the information in your database so it can
be used easily? Work with a partner to create an identification key to help you and
others identify minerals. After you and your partner have completed your
identification key, see if other students can figure out how to use it. Can they
suggest ways to improve it?
Extending
Figure 2.9 Native copper
Use a rock and mineral field guide to find out about the
properties of copper and diamond. List some of the
commercial uses for these two minerals. How are their
properties related to these uses?
Figure 2.10 Raw diamonds
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PROSPECTING
FOR
WEALTH
Identifying rocks and minerals isn’t just a fascinating hobby; it’s big
business! Canada is the world’s largest mineral exporter and is one
of the world’s leading producers of gold, copper, nickel, zinc, lead,
silver, iron ore, asbestos, potash, sand, gravel, and clay. There are
over 500 mines and quarries scattered across Canada, with mining
operations taking place in every province and territory.
Figure 2.11 These
diamonds are from
Canada’s first diamond
mine, the Ekati mine near
Lac de Gras, Northwest
Territories. It began
operations in 1998.
Figure 2.12 The Highland
Figure 2.13 Alberta’s coal mines produce
nearly half of all of Canada’s coal. (It is
estimated that there is enough coal in
Alberta to last about 1000 years at
current rates of use.) The Highvale mine
pictured above is 80 km west of
Edmonton. It is Canada’s largest coal
mine.
Valley open-pit mine near
Kamloops, British
Columbia, is the largest
base metal mine in Canada.
It produces copper and
molybdenum ore.
CHECK
AND
REFLECT
1. One of the steps in identifying a rock is to identify the minerals
it contains. For example, granite is made of quartz, feldspar, and
mica. If you were given an unknown rock, how would you use
what you learned in this section to identify it?
2. The properties of minerals are useful for more than just
identifying them. Sometimes, properties make a mineral
valuable. For example, colour is important in gemstones. What
other property that you learned about in this subsection might
make a mineral useful or valuable?
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